Iboost power question

My iboost setup is new. I love it, obviously. But can anyone tell me how much energy in KWH (in their experience) it takes for an iboost to heat a large tank (250l) from cold? Mine put over 13 kwh into it one day and the water was lovely and warm, but I still don't know how much energy it would take two 3000W immersions to heat a tank of water.
London. 6.4kwh system, South facing. 16 Hyundai 400kw all black panels w/ optimisers, 6kw Solaredge HD Wave inverter, Solar Iboost with two immersion heaters on one 240l hw tank. Octopus Flux. Ivar 5 Wood Burning Stove. Leaf 62kwh plus Zappi. Two chickens: 1 Light Sussex, 1 Speckled Rock. Omlet walk-in run. Approx 1.5 eggs per day egg generation rate using Marriage's organic layers pellets.

Comments

  • JKenH
    JKenH Posts: 4,792 Forumite
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     28.6 kWh is needed to heat 250litres of water from 10c to 60c so it would take around 9.5 hours. (The iBoost will only send power to one heater at once.) 
    Northern Lincolnshire. 7.8 kWp system, (4.2 kw west facing panels , 3.6 kw east facing), Solis inverters, Solar IBoost water heater, Mitsubishi SRK35ZS-S and SRK20ZS-S Wall Mounted Inverter Heat Pumps, ex Nissan Leaf owner)
  • Reed_Richards
    Reed_Richards Posts: 4,153 Forumite
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    edited 4 March 2022 at 5:21AM
    IF you have a blending valve on your hot water outlet (or on every hot tap) then it make sense to heat the tank as hot as you can without triggering the safety cut-out.  To about 75 C, perhaps?
    Reed
  • Benny2020
    Benny2020 Posts: 525 Forumite
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    I have a 140 litre tank and a 28 inch top mounted immersion and it takes 4 to 5 kwh a day to get to 70 degrees,
  • Solarchaser
    Solarchaser Posts: 1,663 Forumite
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    JKenH said:
     28.6 kWh is needed to heat 250litres of water from 10c to 60c so it would take around 9.5 hours. (The iBoost will only send power to one heater at once.) 
    I think you were maybe thinking of a 500l tank mate?

    I've been looking into tanks a bit lately so this post caught my eye

    West central Scotland
    4kw sse since 2014 and 6.6kw wsw / ene split since 2019
    24kwh leaf, 75Kwh Tesla and Lux 3600 with 60Kwh storage
  • QrizB
    QrizB Posts: 13,822 Forumite
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    It takes 0.6 kWh to heat 10 litres of water by 50C.
    Multiply that to suit the size of your tank.
    N. Hampshire, he/him. Octopus Go elec & Tracker gas / Shell BB / Lyca mobi. Ripple Kirk Hill member.
    2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 3.6kw inverter. 30MWh generated, long-term average 2.6 Os.
    Taking a break, hope to be back eventually.
    Ofgem cap table, Ofgem cap explainer. Economy 7 cap explainer. Gas vs E7 vs peak elec heating costs.
  • JKenH
    JKenH Posts: 4,792 Forumite
    First Anniversary Name Dropper First Post
    JKenH said:
     28.6 kWh is needed to heat 250litres of water from 10c to 60c so it would take around 9.5 hours. (The iBoost will only send power to one heater at once.) 
    I think you were maybe thinking of a 500l tank mate?

    I've been looking into tanks a bit lately so this post caught my eye

    My mistake. I think I worked it out from 0-100C and forgot to halve it. 
    Northern Lincolnshire. 7.8 kWp system, (4.2 kw west facing panels , 3.6 kw east facing), Solis inverters, Solar IBoost water heater, Mitsubishi SRK35ZS-S and SRK20ZS-S Wall Mounted Inverter Heat Pumps, ex Nissan Leaf owner)
  • NoobSolar
    NoobSolar Posts: 117 Forumite
    First Anniversary First Post
    Thanks for so many useful comments. I am finding similar things : my iboost is putting through between 7 and 9 kwh typically, on days where we don't quite run out of hot water, in a 240 litre tank. It did 13kwh once on a cold tank also used for a midday bath.
    London. 6.4kwh system, South facing. 16 Hyundai 400kw all black panels w/ optimisers, 6kw Solaredge HD Wave inverter, Solar Iboost with two immersion heaters on one 240l hw tank. Octopus Flux. Ivar 5 Wood Burning Stove. Leaf 62kwh plus Zappi. Two chickens: 1 Light Sussex, 1 Speckled Rock. Omlet walk-in run. Approx 1.5 eggs per day egg generation rate using Marriage's organic layers pellets.
  • Verdigris
    Verdigris Posts: 1,725 Forumite
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    If nothing else, this thread is a timely reminder of how much energy water-heating gobbles up.
  • Solarchaser
    Solarchaser Posts: 1,663 Forumite
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    Yes Indeed.
    Got an email from octopus to say gas will go over 7p in a couple of weeks time.
    With gas 75% efficient and electric at 99% for heating, I think it's definitely time to switch to electric water heating... and maybe electric house heating 
    West central Scotland
    4kw sse since 2014 and 6.6kw wsw / ene split since 2019
    24kwh leaf, 75Kwh Tesla and Lux 3600 with 60Kwh storage
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